(i) Field of The Invention
This invention relates to stable, low viscosity cosmetic emulsions which have the skin refreshed upon application thereof without becoming sticky after the application and which have appropriate moisture retentivity. The invention also relates to a method for making such emulsions.
(ii) Description of the Prior Art
In general, cosmetic emulsions consist of water, oils and emulsifiers and, when applied to the skin, they form an oil film on the surface of the skin. By the coverage with the oil film, a percutaneous water loss is so suppressed that moisture in the horny layer is appropriately retained. The moisture-retentive effect depends on the type and amount of the oil, and thus the type and amount of the oil are suitably controlled according to the purposes.
In order to attain less stickiness and refreshness to the touch by the use of emulsions, it is necessary to reduce the amount of oils and use oils which are less sticky.
The polysiloxane of the general formula (II), (III) or (IV) indicated hereinafter (hereinafter referred to silicone oil) is able to form a uniform thin film on the skin and is suitable as an oil imparting the stickness-free smoothness to the touch. However, the silicone oil is rather poor in compatibility with ordinary surface active agents and other oils and has very poor ability of being emulsified, which makes it very difficult to obtain uniform, fine emulsions.
Better stability against coalescence and creaming is otained when emulsified particles are more uniform and finer. This tendency becomes more pronounced particularly when the viscosity of the system is low. The state of emulsification takes part in the appearance or whiteness of an emulsion. In this sense, optimal results are obtained when the particle size is in the range of from 0.2 to 2 .mu.m. At a smaller particle size, there is obtained a transparent, pale microemulsion. Over the above range, a semitransparent , greyish emulsion is obtained.
In order to further impart refreshness at the time of application, the cosmetic system is preferred to contain ethyl alcohol. In general, addition of ethyl alcohol results in a considerable lowering of emulsion stability of the system.
The emulsion system having such properties as described above should satisfy the following requirements: ethyl alcohol is contained in an aqueous phase; an oil being emulsified is mainly composed of silicone oil and is contained in small amounts; and the system is low in viscosity and has emulsified particles which are fine and uniform in size. However, known emulsification techniques cannot satisfy all the above requirements at the same time.